Denchai Worasawate

A graphical user interface (GUI) for plane-wave scattering from a conducting, dielectric, or chiral sphere

Various numerical techniques have been developed for modeling electromagnetic field propagation in various novel complex media. The validity of these techniques is usually verified by comparison to the exact solutions of canonical problems. Recently, research has focused on chiral media, a subclass of materials known as bianisotropic materials, and numerical techniques have been developed in order to calculate the interaction of electromagnetic fields with chiral objects. One canonical problem for these techniques is plane-wave scattering from a chiral sphere. This work presents a software package that displays and saves the calculated data for the scattering from a chiral, dielectric, or perfectly conducting sphere using a friendly graphical user interface (GUI).

A Switched-Beam Antenna Using Circumferential-Slots on a Concentric Sectoral Cylindrical Cavity Excited by Coupling Slots

This paper presents a switched-beam antenna using circumferential-slot on a concentric sectoral cylindrical cavity excited by coupling slots to operate at 5.8 GHz. The advantages of this antenna are conformal structure, high directivity and capable of switched-beam pattern in six directions. The antenna design starts from a single sector which is capable of switching between radiating and non-radiating modes. The L-shaped coupling slots are proposed to accommodate the switching circuit. Each RF switch is made of two PIN diodes connected in a reverse series connection and placed across the slot at the appropriate location. Subsequently, the exciting probe is designed for matching TM01 mode of the circular waveguide. The measured results of the proposed antenna give a gain of 7 dBi and |S11| less than −20 dB at 5.8 GHz. This antenna is suitable for base station applications that require the switched-beam pattern in the azimuthal plane. Received 22 July 2011, Accepted 25 August 2011, Scheduled 1 September 2011 * Corresponding author: Denchai Worasawate (fengdcw@ku.ac.th). 128 Wounchoum et al.

An improvement of an RFID indoor positioning system using one base station

The proliferation of mobile computing devices and wireless positioning networks has fostered a growing interest in location-aware systems and devices. Most technologies such as Radio Frequency IDentification (RFID), RADAR, etc, use at least three Base Station (BS) for calculating position of target objects. This paper describes an improvement of the previous OneBS algorithm [13]. The proposed system uses only one BS based on the RFID infrastructure for positioning target tags amid the clutter of indoor interference environments. We proposed to fuse the Round-trip Time of Flight (RTOF) and the Received Signal Strength (RSS) in the positioning algorithm. Both information are kept in an intersection Box (iBox). The RTOF information is used to focus a target tags position among groups of four-nearest-neighbor reference tags kept within iBox. Then, the RSS information is weighted using the weighted center of gravity technique to estimate a location of the target tags. Our experiments are based on Three Dimension (3D) materials within interference environments. The interference environments are simulated based on Uniform Geometrical Theory of Diffraction (UTD), for measuring signals in each specific area. Our proposed algorithm gains 50 percents better average distance error compared to the OneBS algorithm.

Affordable Ink-Jet Printed Antennas for RFID Applications

With the increasing demands of radio-frequency identification (RFID) applications, an alternative ink-jet printing technique for RFID tag antenna is demonstrated. Commercially available ink-jet printers are adapted for conductive printing, in order to minimize manufacturing cost. Paper-based dipole antenna and dipole with a tuning stub antenna were designed. The antennas were ink-jet printed and assembled with RFID chips. The performances of the fabricated tags were measured through the reading range. With reference to equivalent isotropically radiated power of 4 W at 923 MHz, the reading range of tag with dipole antenna is around 9 m and of tag with dipole with a tuning stub is nearly 13 m. These performances are comparable to those of commercial tags. The advantages of the proposed printing technique are simplicity, flexibility and, more importantly, affordability. The technique can, in addition, contribute to further development and enhance extension of RFID applications.

A TWO-SLOT ARRAY ANTENNA ON A CONCENTRIC SECTORAL CYLINDRICAL CAVITY EXCITED BY A COUPLING SLOT

A two-slot array antenna on a concentric sectoral cylindrical cavity excited by a coupling slot is investigated. The electromagnetic fields and Q factors for the first few modes of a concentric sectoral cylindrical cavity are presented. It shows that the appropriate mode for a slot array antenna on a concentric sectoral cylindrical cavity is the TM110 mode. The correlations between each mode distribution and the magnetic field distributions inside the cavity are presented. The antenna design and the parametric study of a two-slot array antenna on a concentric sectoral cylindrical cavity for a single sector are illustrated. Simulated results are validated by measurements. The results provide useful information for the design of a switched-beam slot array antenna on the concentric sectoral cylindrical cavities.

Electromagnetic resonances and Q factors of a chiral sphere

A study of electromagnetic resonances of an isotropic chiral sphere is presented. The characteristic equation of a chiral sphere, which is complex and transcendental, is obtained by forming solutions of the electromagnetic field for a chiral sphere in terms of the spherical vector wave functions. The characteristic equation is solved by using a computer. Resonant frequencies and Q factors of the first few modes for relative permittivities of two and ten are reported and discussed. These modes are hybrid modes. They are classed as either hybrid electric (HE) modes or hybrid magnetic (HM) modes. Chirality is observed to have a significant effect on the resonances of a sphere.

Radiation Characteristics of Two-Slot Array Antenna on a Concentric Sectoral Cylindrical Resonator Excited by a Coupling Slot

This paper presents the radiation characteristics of two-slot array antenna on a concentric sectoral cylindrical resonator excited by a coupling slot. The magnetic fields inside the sectoral cylindrical resonator for the first few modes are presented with sectoral angle of 60 degrees. It shows that the appropriate mode for a slot array antenna on a concentric sectoral cylindrical resonator is the TM110 mode. The radiation patterns of two-slot array antenna on a concentric sectoral cylindrical resonator for single sector are illustrated. The location of the coupling slot is considered to find the appropriate radiation pattern. The results provide useful information for the design of switched-beam array antenna on the concentric sectoral cylindrical resonators.

Simulated results for single layer dual mode antennas for UHF RFID tag using open stubs

This paper proposes a single layer structure of a tag antenna for UHF RFID. The antenna can be used in both metallic and non-metallic surfaces. The antenna operates as a microstrip antenna when it is attached to a metallic surface and operates as a dipole antenna when it is attached to a non-metallic surface. The antenna is designed on Teflon substrate with the thickness of 1.52 mm to match NXP UCODE G2XL. The RFID-chip impedance is a resistor of 1385 ohm in parallel with a capacitor of 1.16 pF. This gives the impedance of 16-j147 ohm at 922.5 MHz. The simulated antenna impedance and reading range of the antenna are reported.

A simple switched beam antenna system for a beacon node localization in wireless sensor networks

This work presents a simple switched beam antenna system for the localization system in wireless sensor networks (WSNs). The element patterns are chosen for the requirements. A simple beamforming network is fabricated and tested. The antenna patterns for the system are numerically computed in unbounded free space and compared with the ones measured in the indoor environment. The results show that the system provides space diversity in the indoor environment. This space diversity can be used in the localization algorithm to improve its accuracy.

Toward Optimal Computation of Ultrasound Image Reconstruction Using CPU and GPU

An ultrasound image is reconstructed from echo signals received by array elements of a transducer. The time of flight of the echo depends on the distance between the focus to the array elements. The received echo signals have to be delayed to make their wave fronts and phase coherent before summing the signals. In digital beamforming, the delays are not always located at the sampled points. Generally, the values of the delayed signals are estimated by the values of the nearest samples. This method is fast and easy, however inaccurate. There are other methods available for increasing the accuracy of the delayed signals and, consequently, the quality of the beamformed signals; for example, the in-phase (I)/quadrature (Q) interpolation, which is more time consuming but provides more accurate values than the nearest samples. This paper compares the signals after dynamic receive beamforming, in which the echo signals are delayed using two methods, the nearest sample method and the I/Q interpolation method. The comparisons of the visual qualities of the reconstructed images and the qualities of the beamformed signals are reported. Moreover, the computational speeds of these methods are also optimized by reorganizing the data processing flow and by applying the graphics processing unit (GPU). The use of single and double precision floating-point formats of the intermediate data is also considered. The speeds with and without these optimizations are also compared.